1. Field of the Invention
The invention relates generally to the field of solids separation through the use of a gyratory sifter. More specifically, the invention relates to structures for sifter screens and product discharge outlets for such sifters having higher efficiency and product cleanliness.
2. Background Art
Screen type separators are used in a variety of applications for separating solids by size. These applications include separating particles of sugar, flour, sand and various chemical powders. Screen type separators typically include one or more screens. Particles are applied to the screen from above and the screen is caused to move in a selected pattern. Particles larger than the screen openings (“mesh”) typically remain above the screen surface for discharge in a respective product outlet (hereinafter “large particle size outlet”), while particles smaller than the mesh will pass through the screen and will be directed to another product outlet (“small particle size product outlet”) and/or a further screen for additional size separator. In single screen separator operations there will be two outflows of particulate product, one being the particles held back by the screen and the other containing the particles that pass through the screen. The outflows are typically conducted through respective product outlet conduits. An example of a separator is described in U.S. Pat. No. 5,951,864 issued to Hazrati et al.
In sanitary processing operations or where the particulate product is expensive, it is desirable to have a minimum residue left on the screen after screening operations are completed. Conventional separators such as the one shown in the Hazrati et al '864 patent have a gap between the screen frame and the separator wall that can be as much or more than ¼ inch. The gap area tends to accumulate product, lessening the yield efficiency of the separator and creating sanitation problems in the case of processing animal or human consumables such as food and pharmaceutical products. Structures known in the art for reducing or eliminating the foregoing gap require a ledge inside the product discharge outlet, and such ledge inhibits product discharge.
There continues to be a need for high efficiency, sanitary separators for use with high value and/or human consumable products.